This invention relates to a teleprinter for texts in alphabets of latin and arabic characters, including an alphanumeric keyboard, a printer adapted to print selectively in either of said two alphabets, and letter spacing means.
Normally for telecommunications in the two alphabets, each teleprinting station must be provided with two separate apparatus adapted to be selectively connected to the network of the teleprinting system. There are also known dot printers adapted to be controlled so as to print selectively according to either of two alphabets.
One object of the invention is to provide a bialphabetic teleprinter, wherein the alphabet can be selected through the network.
According to the invention, we now provide a bialphabetic teleprinter of the above kind, which is characterized by means for recognizing sequences of signals to condition the teleprinter to operate both in sending and receiving according to one of said alphabets and to condition said spacing means to accordingly select the direction of letter spacing movement.
The invention includes also an improved device for generating and either displaying or printing characters of alphabets of arabic type, for example Farsi, Urdu, Pakistani, etc.
As known, the alphabet of these languages, having a limited number of phonetic letters, generally 28 letters, presents a great variety of written characters, since many letters are normally written in different forms according to whether they are placed at the beginning of the word, in the body of the word, at the end of the word, or isolated. Moreover, these languages present various syllabic combinations, in which the syllabic components differ from the corresponding letters either isolated or combined with other signs. For instance the syllable constituted by the letter "1" (1am) and by the letter "a" (alef) presents a form in which the letter "a" is deformed and intertwined with the letter "1," as will be better seen hereinafter.
With the development of office machines in general, and of the typewriter in particular, it has been sought to simplify the arabic alphabet writing, by drastically reducing the number of written characters to the detriment of the writing refinement, so as not to increase the complexity of the keyboard or the number of keys available to the operator.
In the conventional typewriters some characters of the alphabet can be written only in two different forms: one for the characters in the body of the word and the other for the end-of-the-word characters, while for the syllable "1a" a special key is often foreseen, which commands the writing of the syllable with a unique writing character.
In such typewriters generally the two forms of the same letter are written by depressing the same key, upon operating a shift key, as occurs for the capital and small letters of the latin alphabet.
Since the letters have, in the end-of-the-word form, a width considerbly larger than in the other letters, such typewriters are normally provided with a variable spacing device, generally able to command, besides the normal spacing, a double-spacing corresponding to this end-of-the-word letter.
In the teleprinter fields, arabic language writing has been further sacrificed to the limit of intelligibility, because of the reduced number of codes in the 5 bit telegraphic system. As known, this codification can give only 32 combinations, which are doubled with the use of the shift. However, since many codes are used for the numerals, for punctuation and special signs and for the various machine functions, it is not possible to obtain two writing forms of the arabic alphabet letters, such as has been relinquished for the lower case letters in the latin alphabet.
The problem of arabic alphabet teleprinters is also found again in the printers and displays of other apparatus, such as electronic calculators, accounting systems, terminals for data transmission, in which the characters are generally identified by code signals, the number of which is limited.
Various apparatus have been proposed to improve the writing of arabic languages by office machines. In a known proposal for typographic composing machines for arabic texts the signals given by a tape reader are sent simultaneously to a memory and to a shift register connected to this memory. In such a way the memory presents the recording of a character sequence, which is used to define the form that one character must have on the basis of its position in the word, the possible connection signs between the letters, and the spacing corrections to justify the end of line, which is the left end in the arabic writing. This proposal, however, is too sophisticated and not suitable for office machine printers because of the high number of characters and keys needed.
In another known printer, the letters having two forms are represented by a short character and a long character. A memory comprising two registers stores a sequence of two characters, while a decoding circuit recognizes when a space is found in one of the two registers, in order to choose for the letter of the other register the long character instead of the short character. This proposal also requires a very large number of characters, substantially equal to those of a typewriter, and the possibility of letter spacing the carriage one or two steps according to whether a short or a long character is printed. Therefore, this solution is not suitable for printers controlled by code combinations in general and for teleprinters in particular. Furthermore, this printer does not allow obtaining the syllabic characters, such as the arabic syllable "1a", in which a part of the character, at least, differs from the corresponding letter when it is placed in other sequences.
Accordingly, another technical problem solved by the invention is to create a display or text printing device in arabic characters, which does not require any added code for the output of the additional characters and which reduces these characters to a minimum.